This invention relates to a switched-mode power supply circuit comprising a series arrangement of a controllable switch and an inductive element coupled between the terminals of a DC input voltage, a rectifier coupled to the inductive element for making a DC output voltage available at a load connected thereto and a control circuit for rendering the switch alternately conductive and non-conductive, the voltage across the inductive element having a given polarity when the rectifier is conductive.
A power supply circuit of this type is known from European Patent Specification 155,369. This known power supply has a circuit for preventing the inductive element from being saturated. For this purpose the magnetic flux in the inductive element is measured and the conductivity time of the controllable switch is controlled by the measuring signal obtained such that the flux remains at an admissible level. The circuit for this power supply is rather complicated.